The present invention relates to devices for performing chemical and biochemical assays, particularly for medical/health purposes. More particularly but not exclusively, it relates to devices for performing pregnancy tests, especially such devices for non-professional use.
It is well known for women to determine if they are pregnant using specialist test devices intended for personal use without the assistance of medical professionals (such devices are generally known as home pregnancy test kits). These devices are usually based on a biochemical immunoassay, testing for the presence of elevated levels of the hormone human chorionic gonadotrophin (hCG) in body fluids, such as urine. The hCG hormone is generated from the very early stages of pregnancy, and so is a very useful indicator species. The immunoassay is generally based on the use of antibodies to hCG and of antigens adapted to couple with such antibodies, at binding sites on the antibody known as epitopes.
The pregnancy test devices first made available relied on urine permeating along a test strip of paper or similar material. A reservoir of hCG antibodies bound to a coloured particulate material (such as colloidal gold or pigmented latex) is encountered first. If hCG is present, the antibodies couple thereto, forming a complex which is carried along the test strip. Further along the test strip is a transverse linear zone of an anchored reagent to which the hCG/antibody complex will bind. Thus, if hCG is present in the urine, the hCG/antibody complex and the associated coloured material will accumulate in this zone, forming a visible coloured line across the test strip.
This approach is widely used, but has led to some problems in practice. In the very early stages of pregnancy, hCG levels are relatively low, and the coloured line may well be faint. This can lead to both false positive and false negative results (reviews have indicated better than 97% accuracy when used by experienced technicians, but as low as 75% when used by the general public). Some users apparently have difficulty in interpreting the presence of a line, even when hCG levels are high.
An alternative approach has thus been to measure the hCG/antibody levels electronically (e.g. by colorimetry), and to use the measured levels to trigger verbal messages on a display screen, such as “Pregnant” or Not Pregnant”. These devices remove much of the human error from the procedure, but are more expensive, due to the need to provide a sensor system, a control chip, a display screen (e.g. an LCD display) and a power source. Additionally, these components are not practical or economic to recycle, but will not break down in landfill or other waste disposal routes.
It would therefore be beneficial if test devices could be produced that gave similarly definite results but without requiring expensive and environmentally unfriendly components.
Tens of millions of home pregnancy test kits of all types are produced, used and discarded every year. There are hence significant waste disposal problems with all current forms of pregnancy testing device, even the non-electronic types.
A further issue is hygiene. At present, it is necessary to dip an end of the test device into a retained urine sample, or more usually the user urinates directly on to the end of the test device. In each case the use should then replace a plastics cap over the urine soaked end of the test device. These caps are a snug fit to obviate leakage, but if the user is not completely accurate in replacing the cap, and inadvertently touches the urine-soaked end of the test strip, or if the user places the used test device on an unsterilised surface before replacing the cap, cross-contamination may occur, which may effect the result of the test. This is also a problem requiring attention.
While the above discussion is expressed in terms of pregnancy tests, there is now a wide range of further, similar assay tests for a variety of medical conditions, working on the immunoassay principle to test urine, blood or other body fluids. In each case, the above problems with accurate and clear display of the results, and with disposal of used test devices, will also apply.
For immunoassay tests for serious conditions such as HIV/AIDS, overspill of test fluids could be particularly undesirable and hazardous. Nevertheless, test devices for such conditions will be required to be usable in non-laboratory, non-ideal conditions, particularly in the developing world.
It is hence an object of the present invention to provide an immunoassay testing device, particularly a pregnancy testing device, that obviates some or all of the above drawbacks of existing devices.